/in/foo.c: In function 'insert':
/in/foo.c:28:12: warning: array subscript has type 'char' [-Wchar-subscripts]
    s[k+1]=s[k];
            ^
/in/foo.c:29:4: warning: array subscript has type 'char' [-Wchar-subscripts]
   s[j]=',';
    ^
/in/foo.c: At top level:
/in/foo.c:34:6: warning: return type of 'main' is not 'int' [-Wmain]
 void main()
      ^~~~
/in/foo.c: In function 'main':
/in/foo.c:39:2: error: too many arguments to function 'insert'
  insert(s,num);
  ^~~~~~
/in/foo.c:20:6: note: declared here
 void insert(char s[])
      ^~~~~~